1. Field of the Invention
This invention relates to a dielectric ceramic composition utilizable as a material for dielectric substrates used in dielectric resonators and electronic equipment.
2. Description of the Prior Art
In high-frequency regions, dielectrics have been hitherto applied, e.g., to impedance matching of microwave circuits and to dielectric resonators. In particular, with recent progress in techniques for the integration of microwave circuits, energetic efforts are being directed to making devices compact by using a dielectric resonator making use of high-permitivity and low-loss dielectric ceramics for the purpose of, e.g., stabilizing frequencies of bandpass filters or oscillators, and it is sought to provide a dielectric ceramic composition having a high permitivity (or dielectric constant) and a high unloaded Q, having a low temperature coefficient of resonant frequency (.tau.f) and also capable of varying the respective characteristics over a wide range.
Now, as materials for these dielectrics, BaO-TiO.sub.2 dielectric ceramics [H. M. O, Bryan, Jr., Thomson, Jr. and J. K. Plourde: J. Am. Ceram. Soc. 57 (1974) 450] and those part of which has been replaced with other element, and also those in which TiO.sub.2 with a negative value and a dielectric ceramic or glass with a positive value are used in combination so that the temperature coefficient of resonant frequency (.tau.f) can be controlled have been utilized.
The above conventional materials, however, have so low a dielectric constant and unloaded Q or so high a temperature coefficient of resonant frequency (.tau.f) that they have a difficulty in their practical use, bringing about various problems. In order to solve such problems, a BaO-TiO.sub.2 -Nd.sub.2 O.sub.3 dielectric ceramic composition (Japanese Patent Publication No. 60-41633) and a BaO-TiO.sub.2 -Nd.sub.2 O.sub.3 -Bi.sub.2 O.sub.3 dielectric ceramic composition (Japanese Patent Publication No. 59-51091) have been proposed. The former, however, has so high a temperature coefficient of resonant frequency (.tau.f) and the latter has so low an unloaded Q with respect to specific dielectric constant that they have been still unsatisfactory for responding the demands for making the required characteristics greater in variety.